What's an idiomatic way to print an iterator s

问题:

I just want a space separated String of the argument variables obtained from std::env::args(), which I've been creating using the fold function like this:

std::env::args()
    .fold("".to_string(), |accum, s| accum + &s + " ")

However this creates an extra space at the end which is unwanted. I tried using the truncate function, but truncate doesn't return a String, just modifies the existing String, and also this would require the creation of an intermediate binding in order to use the String's len() call to define how long the truncated String should be (which itself would require an intermediate binding due to Rust's current lexical borrowing rules I believe!)

回答1:

What's an idiomatic way to print all command line arguments in Rust?

fn main() {
    let mut args = std::env::args();

    if let Some(arg) = args.next() {
        print!("{}", arg);

        for arg in args {
            print!(" {}", arg);
        }
    }
}

Or better with Itertools' format:

use itertools::Itertools; // 0.8.0

fn main() {
    println!("{}", std::env::args().format(" "));
}

I just want a space separated String

fn args() -> String {
    let mut result = String::new();
    let mut args = std::env::args();

    if let Some(arg) = args.next() {
        result.push_str(&arg);

        for arg in args {
            result.push(' ');
            result.push_str(&arg);
        }
    }

    result
}

fn main() {
    println!("{}", args());
}

Or

fn args() -> String {
    let mut result = std::env::args().fold(String::new(), |s, arg| s + &arg + " ");
    result.pop();
    result
}

fn main() {
    println!("{}", args());
}

If you use Itertools, join is useful:

use itertools::Itertools; // 0.8.0

fn args() -> String {
    std::env::args().join(" ")
}

fn main() {
    println!("{}", args());
}

In other cases, you may want to use intersperse:

use itertools::Itertools; // 0.8.0

fn args() -> String {
    std::env::args().intersperse(" ".to_string()).collect()
}

fn main() {
    println!("{}", args());
}

Note this isn't as efficient as other choices as a String is cloned for each iteration.

回答2:

Here is an alternative for

I just want a space separated String of the argument variables obtained from std::env::args()

fn args_string() -> String {
    let mut out = String::new();
    let mut sep = "";
    for arg in std::env::args() {
        out.push_str(sep);
        out.push_str(&*arg);
        sep = " ";
    }
    out
}

pub fn main() {
    println!("{}", args_string());
}